Phosphoinositides (PIs), which are phosphorylated derivatives of phosphatidylinositol, are essential in eukaryotic cells, regulating nuclear processes, cytoskeletal dynamics, signalling and membrane trafficking. Among the enzymes involved in PI metabolism, PI3-kinases (PI3K) have attracted special attention because of their oncogenic properties and potential as drug targets. PI3-kinases phosphorylate phosphatidylinositols or PIs at the 3-position of the inositol ring. (Lindmo et al. Journal of Cell Science 119, 605-614, 2006). The 3-phosphorylated phospholipids generated by PI3K activity bind to the pleckstrin homology (PH) domain of protein kinase B (PKB), causing translocation of PKB to the cell membrane and subsequent phosphorylation of PKB. Phosphorylated PKB inhibits apoptosis-inducing proteins such as FKHR, Bad, and caspases, and is thought to play an important role in cancer progression. The PI3Ks are divided into classes I-III, and class I is further subclassified into classes Ia and Ib. Among these isoforms, class Ia enzymes are thought to play the most important role in cell proliferation in response to growth factor-tyrosine kinase pathway activation (Hayakawa et al., Bioorganic & Medicinal Chemistry 14 6847-6858, 2006). Three frequent mutations in cancer constitutively activate PI3Kα and, when expressed in cells, they drive the oncogenic transformation and chronic activation of downstream signalling by molecules such as PKB, S6K and 4E bp1 that is commonly seen in cancer cells. (Stephens et al., Current Opinion in Pharmacology, 5(4) 357-365, 2005). As such, PI3-kinases are attractive targets for the treatment of proliferative diseases.
There are several known PI3-kinase inhibitors including Wortmannin and LY294002. Although Wortmannin is a potent PI3K inhibitor with a low nanomolar IC50 value, it has low in vivo anti-tumor activity. (Hayakawa et al., Bioorg. Med. Chem. 14(20), 6847-6858 (2006)). Recently, a group of morpholine substituted quinazoline, pyridopyrimidine and thienopyrimidine compounds have been reported to be effective in inhibiting PI3kinase p110α. (Hayakawa, 6847-6858). Oral dosage of a morpholine substituted thienopyrimidine compound (GDC-0941) has shown tumor suppression in glioblastoma xenografts in vivo. (Folkes et al., Journal of Medicinal Chemistry, 51, 5522-5532, 2008). The following publications disclose a series of thienopyrimidine, pyridopyrimidine and quinazoline based PI3-Kinase inhibitors: WO 2008/073785; WO 2008/070740; WO 2007/127183; U.S. Patent Publication 20080242665.

Histone acetylation is a reversible modification, with deacetylation being catalyzed by a family of enzymes termed histone deacetylases (HDACs). HDAC's are represented by 18 genes in humans and are divided into four distinct classes (J Mol Biol, 2004, 338:1, 17-31). In mammalians class I HDAC's (HDAC1-3, and HDAC8) are related to yeast RPD3 HDAC, class 2 (HDAC4-7, HDAC9 and HDAC10) related to yeast HDA1, class 4 (HDAC11), and class 3 (a distinct class encompassing the sirtuins which are related to yeast Sir2).
Csordas, Biochem. J., 1990, 286: 23-38 teaches that histones are subject to post-translational acetylation of the ε-amino groups of N-terminal lysine residues, a reaction that is catalyzed by histone acetyl transferase (HAT1). Acetylation neutralizes the positive charge of the lysine side chain, and is thought to impact chromatin structure. Indeed, access of transcription factors to chromatin templates is enhanced by histone hyperacetylation, and enrichment in underacetylated histone H4 has been found in transcriptionally silent regions of the genome (Taunton et al., Science, 1996, 272:408-411). In the case of tumor suppressor genes, transcriptional silencing due to histone modification can lead to oncogenic transformation and cancer.
Several classes of HDAC inhibitors currently are being evaluated by clinical investigators. Examples include hydroxamic acid derivatives, Suberoylanilide hydroxamic acid (SAHA), PXD101 and LAQ824, are currently in the clinical development. In the benzamide class of HDAC inhibitors, MS-275, MGCD0103 and CI-994 have reached clinical trials. Mourne et al. (Abstract #4725, AACR 2005), demonstrate that thiophenyl modification of benzamides significantly enhance HDAC inhibitory activity against HDAC1.
Certain cancers have been effectively treated with such a combinatorial approach; however, treatment regimes using a cocktail of cytotoxic drugs often are limited by dose limiting toxicities and drug-drug interactions. More recent advances with molecularly targeted drugs have provided new approaches to combination treatment for cancer, allowing multiple targeted agents to be used simultaneously, or combining these new therapies with standard chemotherapeutics or radiation to improve outcome without reaching dose limiting toxicities. However, the ability to use such combinations currently is limited to drugs that show compatible pharmacologic and pharmacodynamic properties. In addition, the regulatory requirements to demonstrate safety and efficacy of combination therapies can be more costly and lengthy than corresponding single agent trials. Once approved, combination strategies may also be associated with increased costs to patients, as well as decreased patient compliance owing to the more intricate dosing paradigms required.